Although the cariostatic value of oat hulls incorporated into the diet of laboratory animals has been known for years, no practical outcome of this knowledge in terms of human populations has occurred so far. This is partially due to the difficulty of using oat hulls in human foods, largely because of their hardness, abrasiveness, off-taste and indigestibility. Another factor has been the difficulty of identifying and isolating the active cariostatic factor(s) from the hulls. In this study attempts will be made to modify oat hulls in order to (a) enhance the release of their active, anticaries ingredient(s), (b) render them more suitable for use in human foods, and (c) increase their overall nutritional and economic value. The modifications which are proposed consist basically of the hydrolysis of the hulls by acids, bases, chelating agents and enzymes. The rationale for these modifications is that the hulls are chiefly composed of cellulose, and thus their hydrolysis can be expected to release some of their other ingredients, reduce their hardness, and improve their taste and digestibility. Support for this concept is suggested by the high cariostatic value of oat hulls relative to occlusal caries, a situation in which it can be assumed that the hulls are retained in the pits and fissures and exposed there to the hydrolysis by plaque metabolites. Additional support is provided by findings of screening tests appended to this application which show a remarkable antiplaque potential for some modified hulls. The experimental part of the project will comprise the modification of the hulls, the determination of the effects of the modified oat hulls upon in vitro plaque formation and characteristics, using the wire plaque technique described by McCabe et al (Arch Oral Biol 12:1653, 1967) and a modification of the same, and the determination of the effects of the modified hulls upon actual caries, body growth and overall health of rats.